The present invention relates to the control of a motor vehicle heating, ventilation and air conditioning (HVAC) system, and more particularly to a hierarchical method of scheduling overrides of various control parameters.
A typical motor vehicle HVAC system has several control parameters that are ordinarily adjusted, either manually or automatically, to achieve a desired cabin air temperature and humidity level. These parameters may include, for example, the position of doors or other mechanisms that regulate the air inlet source and the air discharge temperature and location, the capacity of the refrigerant compressor, and the blower speed. However, many HVAC systems are configured to permit overriding of the normal control settings under certain conditions. For example, most automatic climate control systems allow the driver to manually override the blower speed and the air discharge location, and both manual and automatic systems include a provision for automatically disengaging the compressor clutch when the high side pressure is too high, or during full-throttle engine acceleration. Many other override controls have also been suggested, such as forcing the system into a defrost mode when windshield fogging is likely, forcing the temperature control door to full heat when the engine coolant temperature is too high, and forcing the air inlet control door to cabin air recirculation when an ambient air quality sensor indicates the presence of significant pollution levels. As the control sophistication level increases, there can be conflicting override commands, and there is a growing need for a hierarchical control method for sorting through the various override commands in order to properly adjust the respective control parameters.
The present invention is directed to an improved control method for a motor vehicle HVAC system, where the system includes at least one control parameter that is ordinarily regulated in accordance with a normal control setting, and where override commands for the control parameter are categorized for the purpose of assigning a priority of control. In particular, the override commands are categorized as being related to occupant safety, vehicle safety or occupant comfort. Highest priority is assigned to override commands categorized as being related to occupant safety, second-highest priority is assigned to override commands categorized as being related to vehicle safety, and third-highest priority is assigned to override commands categorized as being related to occupant comfort. An HVAC controller carrying out the control method then regulates the control parameter in accordance with the override command that has been assigned the highest priority.